for CSO Treatment December 2002, the city of Toledo, Ohio, signed a consent decree with the U.S. Environmental

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1 16 August 2007 WWDmag.com WATER & WASTES DIGEST EDITOR SFOCUS A Compact Solution for CSO Treatment By K. Scott Henderson A look at the largest high-rate clarification system for CSO treatment in North America I n December 2002, the city of Toledo, Ohio, signed a consent decree with the U.S. Environmental Protection Agency (EPA) that required the city to update its sewer and wastewater treatment facilities to stop wet weather bypassing of untreated wastewater into the Maumee River. To achieve regulatory compliance associated with combined sewer overflow (CSO) events, it was determined that the Bay View Wastewater Treatment Plant (WWTP) must increase its total treatment capacity from 200 to 400 million gal per day (mgd), or approximately 5.3 times the average dry weather flow rate. 1 Prior to the final design, pilot testing of high-rate clarifier technologies was conducted from December 2002 to February 2003 to determine the feasibility of using this technology to achieve the required effluent criteria for both primary and CSO wastewaters. Based on the results of the pilot study, the DensaDeg high-rate solids contact clarifier, manufactured by Infilco Degremont, Inc., was chosen for the full-scale installation. Based on the design parameters, it was determined that the facility would need six of these clarifiers. In November 2006, the construction of the largest high-rate clarification system for CSO treatment was completed. The overall layout can be seen in Figure 1, and a picture of the constructed facility is shown in Figure 2. The maximum design capacity for the facility is 232 mgd with each of the six high-rate clarifiers having the capacity to treat 38.7 mgd at a surface overflow rate of 47 gpm/ft 2. FIGURE 1: Overall Layout Bay View WWTP Wet Weather Facilities The clarifier The DensaDeg clarifier is a high-rate solids contact clarifier that combines optimized flocculation, internal and external sludge recirculation and lamellar settling to achieve very high hydraulic loadings and treatment efficiencies. It is well proven in the field of physical and chemical treatment of wastewater and drinking water and has been employed for a wide range of municipal and industrial applications. The DensaDeg 2D-100 for physical and chemical treatment of raw municipal wastewater, CSO and sanitary sewer overflows (SSO) combines coagulation, flocculation, static and lamellar clarification, scum removal and sludge thickening in a single treatment unit. Optimized flocculation and solids contact through internal and external sludge recirculation produces dense floc with an extremely high settling rate (typical design rates are 40 gpm/ft 2 with the hydraulic capacity to accommodate rise rates up to 60 gpm/ft 2, with a moderate reduction in treatment efficiencies) without adding ballast materials such as sand. The process Rapid mix. The first step in the clarifier process, coagulation, takes place in a single vessel. A coagulant, either aluminum or iron salt, is injected directly into the inlet pipe, or if possible, upstream in the feed channel. Mechanical mixers cause an intense bulk fluid motion for coagulant dispersion and mixing. The flow then passes to the reactor vessel. Reactor vessel. The reactor vessel is where particle flocculation and densification occurs. The flocculation reaction is optimized in the reactor vessel through the combined effects of internal sludge recirculation, high solids concentration and efficient mixing. A high concentration of solids is maintained in the reactor through external recirculation of settled solids from the clarifier/thickener vessel. Internal recirculation is achieved through an axial flow impeller/draft tube arrangement. Polymer, usually a high molecular weight anionic type, is injected either directly beneath the impeller blades or in the sludge recirculation line. Polymer aids in the flocculation and densification of the coagulated particles. Clarifier/thickener vessel. Quiescent conditions exist in the clarifier/thickener vessel, where the dense floc particles formed in the reactor vessel are allowed to settle and thicken. A circular, picket fence-type scraper mechanism collects FIGURE 2: Bay View WWTP DensaDeg High Rate Clarifier Facility

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3 18 August 2007 WWDmag.com WATER & WASTES DIGEST Heavy-Duty Engineered Wastewater Pumping Systems settled sludge into a center bottom hopper. Thickened sludge (typically 20 to 40 g/l) is pumped to a holding tank and then transferred directly to digesters or dewatering facilities. Additional sludge thickening is generally not required. A separate set of recycle pumps return a portion of the sludge to the reactor vessel. Settled water then flows upward through settling tubes where stray floc is removed. The majority of the solids are removed from the stream prior to entering the lamellar modules. The lamellar tubes act as polishers only and are therefore not subject to clogging. Final clarified effluent collects in a trough for further downstream treatment or discharge. Morris Pumps - Div. Yeomans Chicago Corp. - Aurora, IL USA Write in 726 Write in 734 Operational strategy One of the unique features that the DensaDeg facility provides is the ability to treat both primary and CSO wastewaters. In order to incorporate this flexibility of operation, an operational guideline was created for the Bay View WWTP. Based on the incoming flow and status of the equalization basin volume, multiple modes of operation are available. The excess flows can be directed to the high-rate clarifiers, and effluent produced can then be sent to the activated sludge system. Or, during high flow events, HRC effluent can be directed to the equalization basin, and when the basin reaches design capacity, the flow is then directed to the dedicated wet weather disinfection system and blended with the plant effluent from the dry weather facilities before it is discharged into the Maumee River. The four main operational scenarios are summarized in Table 1. :: Smaller Footprint The AquaDiamond filter offers the benefits of OptiFiber pile cloth media filtration in a lower profile, diamond configuration. This filter easily retrofits into existing traveling bridge sand filters while providing higher hydraulic and solids loading rates in a smaller footprint. ::Plant Profile Fox Metro Water Reclamation District, located in Oswego, Illinois retrofitted three of its nine existing 16' x 112' traveling bridge sand filters with 80' long AquaDiamond cloth media filters to solve its ongoing maintenance and performance issues. The three combined AquaDiamond filters provide a peak flow capacity of 72 MGD, which is almost 2.5 times the hydraulic capacity of the original three sand filters, within the same footprint. The AquaDiamond filters have also proven the ability to perform under higher solids loading conditions than the sand filters, while backwashing less. Fox Metro plans to install two additional AquaDiamond filters in 2007, resulting in a total of five filters with a combined peak flow capacity of 120 MGD. Higher Capacity AQUA-AEROBIC SYSTEMS, INC. P a r t n e r i n g f o r S o l u t i o n s Write in 706 :: :: Benefits Unique OptiFiber pile cloth media Reuse quality effluent Higher solids loading per ft 2 of media Reduced backwash water volume Higher hydraulic loadings Reduced footprint Less maintenance Disk and drum configurations also available :: Applications Municipal and Industrial - Tertiary filtration - Reuse/recycle - Phosphorus removal - New plants and retrofits 6306 N. Alpine Road Rockford, IL PH FX TABLE 1: Operational Strategy Summary Bay View WWTP Scenario Operational Strategies Q = 0 to 130 mgd All flow is treated by the dry weather Bay View WWTP facilities. Q = 130 to 190 mgd Up to 160 mgd is treated by the dry 30 mgd is directed to the highrate clarifier (HRC) facility HRC effluent is routed to the activated sludge system; Q > 190 mgd Up to 160 mgd is treated by the dry & Veq < Vtot Excess flow are directed to the HRC facility; 30 mgd of HRC effluent is routed to the activated sludge system; Remainder of effluent is discharged to the equalization basin. Q > 195 mgd Up to 160 mgd is treated by the dry & Veq = Vtot Excess flows are directed to the HRC facility; 30 mgd of HRC effluent is routed to the activated sludge system; Remainder of HRC effluent is routed to disinfection and blending with effluent from dry weather Bay View WWTP. Vtot = Total volume of equalization basin (25 million gal) Veq = Volume of wastewater in the equalization basin at a given time Performance testing Based on the required operational flexibility of the Bay View WWTP, the performance testing was formulated to simulate the various operational scenarios. Each clarifier was tested individually to assess performance.

4 WATER & WASTES DIGEST WWDmag.com August FIGURE 3: Typical Performance Test Run TSS Removal Efficiency FIGURE 4: Typical Performance Test Particulate CBOD Removal Efficiency TABLE 2: Performance Test Summary - Average Removal Efficiencies and Average Concentrations* TSS CBOD Total P Influent TSS Effluent TSS Influent CBOD Effluent CBOD Influent Total P Effluent Total P Primary treatment performance level 83% 54% 89% Wet weather treatment performance level 1 79% 53% 86% Wet weather treatment performance level 2 70% 46% 72% *Concentrations are in mg/l High Maintenance. Low Maintenance. Some things just require more maintenance than others. Tanks are no different. Choose Aquastore and you get an exclusive glass-fused-to-steel bolted tank that is factory engineered to be the best. Say good-bye to high maintenance construction, cracks, painting, corrosion and rust. A low maintenance Aquastore is easily constructed, never needs repainting and delivers proven lifetime performance. With Aquastore, you can be assured you will get the highest engineered quality, service and product life in storage tanks. For more information visit or call Tanks & Domes Glass Tanks with a Heart of Steel Aquastore is a registered trademark of Engineered Storage Products Company. Write in 720 Write in 705

5 20 August 2007 WWDmag.com WATER & WASTES DIGEST FIGURE 5: Sectional View of DendaDeg 2D-100 The Eclipse Model 705 Transmitter uses revolutionary Guided Wave Radar technology providing unsurpassed accurate measurement even in foam, varying media or applications with coating and buildup. Eclipse transmitters are designed for easy installation and configuration. The compact innovative housing and display makes data easy to read. Guided Wave Radar from STI is engineered to solve the challenges of water and wastewater treatment environments Belmont Road Downers Grove, IL sticontrols.com Write in 716 Write in 718 The first level of performance testing required the units to operate at a flow rate of < 27 mgd (SOR = 32.9 gpm/ft 2 ), the second level of testing required a flow rate of 31 mgd (SOR = 37.5 gpm/ft 2 ), and the third level a flow rate of 38.7 mgd (SOR = 47 gpm/ft 2 ). During the testing of each performance level, samples were taken during each hour of operation to measure TSS, CBOD and total phosphorus. Each clarifier was tested for a six-hour period and figures 3 and 4 ( page 19) show representative runs for an individual DensaDeg unit. Table 2 (page 19) provides a summary of the average removal efficiencies and average concentrations achieved during of the full-scale performance testing. Conclusion The system recently constructed at the Bay View WWTP is the largest high-rate clarification system for CSO treatment in North America. As seen in the performance test data, the DensaDeg can achieve removal efficiencies in the range of 70 to 95% for TSS, 55 to 70% for total CBOD and 70 to 95% for total phosphorus, while operating at high surface overflow rates. These full-scale results confirm those achieved during the pilot testing and meet the design requirements of the facility. This demonstrates that based on the highrate design of the process, large CSO treatment capacity can be achieved in a relatively moderate site area (232 mgd within a 43,500 ft 2 area), thereby providing municipalities with a compact solution for CSO treatment. WWD References Nitz, D. et al. (2004) Session 23: Wet Weather Treatment Issues Wet Weather Treatment Pilot Testing: High Rate Clarification and UV Disinfection in a Cold Climate. WEFTEC 2004, New Orleans, La. Quiet, clean VFD controls Non-pulsating flow Closed piping system Compact heavy duty Ultra-Drive gear joint design Optional slip injection system Twin screw feeder High-efficiency Ultra-Feed rotor Moves a higher percentage of solids longer distances than any other progressing cavity pump! Come see us at Booth #4037 Patented UMOYNO K. Scott Henderson, P.E., is application engineer at Infilco Degremont. He can be reached at 804/ or by at scott.henderson@infilcodegremont.com. For more information, write in 1101 on this issue s Reader Service Card. LEARN MORE For additional articles on this topic, visit: Write in 717